The trend in the field of opto-electronic is towards higher integration, further miniaturization and improved reliability. One important step in this direction is the employment of laser diodes with etched mirror surfaces. The prior known and almost exclusively used cleaved lasers have some drawbacks limiting their utilization in future opto-electronic structures. Cleaved laser bars have to be handled as discrete devices for some of the fabrication steps resulting in inefficient fabrication and testing procedures. In addition, the cleaving technique determines the chip size of a few hundred microns, and therefore makes the integration of additional optical and electronic devices difficult or even impossible.
Fundamental steps towards full wafer processing and therewith higher integration and reduced fabrication costs have been made by the so-called full wafer technology, This technology, which is based on etched laser mirrors, is described in the article "Full wafer technology-A new approach to large-scale laser fabrication and integration", by P. Vettiger et al., IEEE Journal Quantum Electron., Vol. 27, June 1991, pp. 1319-1331.
Full wafer processing (FWP) and full wafer testing (FWT) allow the integration of laser diodes with optical or electrical devices. One important aspect for the integration of opto-electronic devices is their efficient optical coupling to waveguides and other optical components. Most proposals known relate to systems in which cleaved lasers are coupled to optical fibers or waveguides. Therefore the laser and/or the optical waveguide have to be aligned during fabrication or packaging. They can not be made using the same processing steps. Examples are listed below:
In the article "Adjusting the Height of Heat Sink Heterojunction Lasers to Meet up with Optical Couplers and Waveguides", of G. L. Hutchins, IBM Technical Disclosure Bulletin, Vol. 17, No. 10, March 1975, p. 3134, a structure is disclosed in which a discrete cleaved laser is aligned to waveguides by mounting it on top of a mesa heat sink. The height of this mesa is calculated such that the laser is matched to the inputs of the waveguides. PA1 Other methods for coupling beams emitted by a laser into adjacent waveguides is proposed in the article "Offset Laser to Groove Waveguide Coupler", L.D. Comerford et al., IBM Technical Disclosure Bulletin, Vol. 20, No. 4, September 1977, pp. 1601-1608. The different structures shown in this article comprise a GaAs laser or laser array mounted on a silicon substrate adjacent to waveguides. Complicated couplers are employed to couple the light into these waveguides. PA1 In the article "Laser Print Head Employing a Plurality of Lasers per Channel", of J. D. Crow, IBM Technical Disclosure Bulletin, Vol. 20, No. 6, November 1977, pp. 2443-2444 an optical converter is disclosed which comprises waveguides for feeding laser beams into fibers. PA1 Several proposals are disclosed in the article "Interconnection of Optical Fibers to Planar Optical Integrated Circuitry", of E. A. Ash, IBM Technical Disclosure Bulletin, Vol. 13, No. 9, February 1971, pp. 2925-2926. The alignment of the fibers is complicated and time consuming. The losses at the interfaces between laser/waveguide on one hand and waveguide/fiber on the other hand are high. PA1 expensive and time consuming packaging, PA1 complicated alignment, PA1 coupling losses PA1 reduced reliability and performance.
For coupling optical fibers to laser diodes other solutions are known in the art. Most of these coupling techniques employ waveguides between the laser source and the fiber. Two examples are described below:
Some drawbacks of the known coupling techniques, for coupling between lasers and waveguides or lasers and fibers are:
An interesting proposal has been made in the book "Integrated Optics: Theory and Technology", of R. G. Hunsperger, Springer Series in Optical Sciences, Second edition, Springer Verlag, p. 92. There it is described how to butt-couple a waveguide to a laser diode by using piezoelectrically driven micrometer heads, which shows again how complicated the alignment of laser diodes and waveguides is.